Seismogenic structure of the hidden Haicheng fault system in China revealed by seismic observations from 2008 to 2018

The hidden Haicheng fault system is an earthquake-prone zone on the Liaodong Peninsula, China. Its seismogenic structure is still unclear and needs further study. In this study, we used the differential evolution algorithm to invert the waveform data of the 2008 M (sub L) 4.8 Haicheng earthquake and the 2012 M (sub L) 4.8 Gaizhou earthquake and obtained an updated 1D crustal velocity model. The model reveals a low-velocity zone with a depth of 18-24 km below the Haicheng fault zone. Based on the velocity model, we used the arrival-time data to accurately locate the earthquakes that occurred in the Haicheng area from 2008 to 2018. The relocated earthquakes show that the Az 300 degrees -trending Haicheng fault consists of two segments spaced about 2 km apart, namely the western and the eastern segments. They are about 12 and 22 km long and inclined to the northeast with dips of 70 degrees and 80 degrees , respectively. These seismogenic structures of the Haicheng fault zone are important for assessing the future seismic risk in the region.